Electrically scanned microstrip antenna

ABSTRACT

A microstrip antenna including a dielectric layer loaded with a ferrite material disposed between a ground plane and a generally planar or single layer arrangement of electrical conductors constituing both r.f. radiators and r.f. feedlines. Either or both of the r.f. radiators and feedlines include special d.c. circuits for passing d.c. electrical currents. When the d.c. electrical currents are passed through the r.f. radiators, the permeability of the ferrite loaded dielectric is altered thus scanning the resonant frequency of a radiator in accordance with the applied d.c. current or voltage. Furthermore, when the d.c. currents are passed through the r.f. feedline, or portions thereof, the magnetic fields set up in the ferrite loaded dielectric causes controlled phase shifts to occur in r.f. energy passing there along thus effecting controlled phase shifts and hence beam scanning of an array of such radiators as a function of the d.c. current or voltage.

United States Patent [1 1 Munson ELECTRICALLY SCANNED MICROSTRIP ANTENNA[75] Inventor: Robert E. Munson, Boulder, C010.

[73] Assignee: Ball Brothers Research Corporation,

Boulder, C010.

[22] Filed: Apr. 17, 1973 [21] Appl. No.: 352,034

[52] US. Cl 343/787, 343/846, 343/854,

333/84 M [51] Int. Cl. H0lq 1/00, l-lOlq 3/26 [58] Field of Search343/769, 787, 846, 854; 333/84 M [56] References Cited UNITED STATESPATENTS 3,680,136 7/1972 Collings 343/769 3.715.692 2/1973 Reuss 333/31R Primary ExaminerEli Lieberman [451 May 14, 1974 [5 7] ABSTRACT Amicrostrip antenna including a dielectric layer loaded with a ferritematerial disposed between a ground plane and a generally planar orsingle layer arrangement of electrical conductors constituing both r.f.radiators and r.f. feedlines. Either or both of the r.f. radiators andfeedlines include special d.c. circuits for passing d.c. electricalcurrents. When the dc. electrical currents are passed through the r.f.radiators, the permeability of the ferrite loaded dielectric is alteredthus scanning the resonant frequency of a radiator in accordance withthe applied dc. current or voltage. Furthermore, when the d.c. currentsare passed through the r.f. feedline, or portions thereof, the magneticfields set up in the ferrite loaded dielectric causes controlled phaseshifts to occur in r.f. energy passing there along thus effectingcontrolled phase shifts and hence beam scanning of an array of suchradiators as a function of the dc. current or voltage.

12 Claims, 6 Drawing Figures PATENTED RAY I 41974 SHEET 2 OF 2ELECTRICALLY SCANNED MICROSTRIP ANTENNA This application is related tomy co-pending U.S. application Ser. No. 352,005 filed concurrentlyherewith. It is also related to commonly assigned United States Pat. No.3,7l3,l62 and to the commonly assigned copending application Ser. No.99,481 filed Dec. 18, I970.

This invention relates generally to antenna structures utilizing aferrite loaded dielectric layer disposed between a ground plane andanother layer of conductors comprising the antenna elements and/orfeedlines. In particular, it relates to an antenna structure of thiskind wherein the resonant frequency of an r.f. radiator and- /or thebeam direction of an array of such radiators is controlled by passingd.c. electrical currents through the radiator and/or feedlinesrespectively.

The antenna structure to be described below is a form of microstripantenna wherein the actual r.f. feedlines and/or r.f. radiators arepreferably formed on one face of a dielectric sheet using conventionalphotoresist/etching techniques as are used in forming electrical circuitboards.

As will be appreciated by those in the art, it is often desirable toincrease the bandwidth or range of possible operating frequencies forany given antenna structure whether that structure is utilized alone orin an array of similar structures. As will be explained in more detailbelow, when the dielectric substrate ofa microstrip antenna is loadedwith a ferrite material the resonant frequency for the microstripradiator may be altered by passing a direct current through the radiatorthus changing the permeability of the ferrite loaded dielectric in thevicinity of the radiator. Such changes in the relative permeability ofthe dielectric will change the effective electrical length or otherdimension of the microstrip radiator thus altering the operatingfrequency as will become apparent. Accordingly, the antenna structure ofthis invention permits controlled increases in the effective bandwidthfor any given antenna dimensions.

An electronically scanned antenna array is usually a costly and complexapparatus. However, as will be explained in more detail below, theantenna structure of this invention may be formed through economicalprinted circuit board techniques to provide a microstrip antenna arrayhaving a radiation beam direction that may be selectively orcontrollably scanned as a function of a variable voltage or current. Onevariable voltage will permit scanning in one coordinate direction whiletwo variable voltages will permit two dimensional scanning along twocoordinate directions as will become apparent. Accordingly, this antennastructure provides an extremely simple, reliable, and cheap scannablearray. Furthermore, it is extremely simple to operate the scanned arrayof this invention since all that is required is a variable dc. voltageor current. Since techniques are readily available for providingvariable voltages/currents having complex predetermined wave shapes, itshould readily be apparent that the antenna array of this invention maybe easily controlled to follow complex scanning patterns.

Furthermore, since the antenna structure of this invention is extremelythin compared to conventional antenna structures, it is readilyadaptable for use in streamlined vehicles such as airplanes and rocketswhere design considerations necessitate the minimum possibleprotuberance either inside or outside of the vehicular skin. As will beappreciated, since the antenna is really in the nature of a thin printedcircuit board, the whole structure will be flexible if the dielectricmaterial is properly chosen thus making it easy to conform the entireantenna structure with the skin of such a vehicle or to any otherdesired shape.

These and many other objects and advantages of this invention will bemore clearly understood from the following detailed description taken inconjunction with the accompanying drawings, of which:

FIG. 1 is a plan view of an exemplary microstrip antenna array accordingto this invention which permits beam scanning in one dimension bycontrolling a dc. current along portions of the r.f. feedline therein;

FIG. 2 is a cross sectional view of the exemplary antenna array shown inFIG. 1;

FIG. 3 is a sequence of schematic diagrams illustrating the variation ofbeam direction with a dc. current for the exemplary antenna structure ofFIG. 1;

FIG. 4 is an exemplary plan view of one microstrip radiator including adc. circuit for altering its resonant frequency;

FIG. 5 illustrates an exemplary modification of the FIG. 1 embodimentusing switchable diodes to further selectively alter the beam steeringcharacteristics of the array; and

FIG. 6 is a schematic illustration of an exemplary two dimensionalmicrostrip antenna array includingtwo separate dc. current circuits inthe r.f. feedlines for steering the beam direction of the twodimensional array along two coordinate axes.

The printed circuit board 10 shown in FIG. 1 is shown in cross sectionat FIG. 2. Broadly stated, it comprises the usual printed circuit boardconstruction wherein a conductive layer 12 is selectively etched awayfrom a dielectric layer 14 to result in a generally planar or singlelayer arrangement of electrical conductors on top of the dielectricsubstrate 14. In the case of this invention, the planar arrangement ofconductors 12 comprises r.f. feedlines as well as r.f. radiator sectionsand superposed d.c. electrical circuits as will be explained. Thedielectric substrate 14 has been loaded with conventional microwavequality ferrite materials as indicated in FIG. 2 and is disposed betweenthe planar arrangement of electrical conductors 12 and a ground planesurface of electrically conducting material 16. As will be appreciatedby those in the art, the ground plane 16 may, in fact, comprise a layerof conductive material adhered to the backside of the dielectric layer14 thus being co-extensive with the dielectric substrate 14. On theother hand, the ground plane 16 might also comprise part of a conductingvehicular sur face such as an airplane or missile skin, etc., as will beappreciated.

As indicated in FIG. 2, the ferrite loaded dielectric 14 may comprise aconventional dielectric material in which conventional microwave qualityferrite powder has been dispersed by conventional techniques.Alternatively, it is possible to load the dielectric substrate with asheet of ferrite material as will be apparent to those in the art. Inthe preferred embodiment, the planar or single layer arrangement ofelectrical conductors 12 is formed by conventional photo resist-chemicaletching processes commonly used in the manufacture of printed circuitboards.

As seen in FIG. 1, a linear array of microstrip radiators N N N and N,is provided. Each of these radiators is fed from an r.f. feedlineemanating from an overall corporate feedline structure wherein theoriginal r.f. input signal at 18 is first divided at point 20 into twoequal power signals as should be apparent. In the absence of any d.c.electrical current (as will be described in more detail below), thesedivided half power signals will also be of equal phase relative to oneanother as they travel along the corporate structure r.f. feedline.

These half power signals are again divided at points 22 and 24 intoquarter power signals of equal power and equal relative phases which arethen fed directly to the microstrip radiators as shown in FIG. 1.Accordingly, as will be appreciated, in this case of Zero d.c. current,all elements of the linear array will be fed with equal power and equalrelative phase signals so that the resultant radiation will be a highgain beam pattern directed normally to the plane of the array and as isschematically illustrated in the top line of FIG. 3.

Ferrite materials have been used in the past to cause relative phaseshifts in r.f. signals as shown for instance in United States Pat. No.3,553,733 to Buck and in United States Pat. No. 3,377,592 to Robieux etal. However, these prior structures have involved bulky waveguidesand/or external electromagnet assemblies that have made them relativelycomplex and costly.

It has now been discovered that the antenna structure of this inventionutilizing a ferrite loaded dielectric may be conveniently modified toproduce the necessary phase shifts between the array radiators thusachieving beam steering capability for the array. For example, as shownin FIG. 1, a variable d.c. electrical current source 26 is connected toa d.c. circuit within the generally planar arrangement of electricalconductors 12 for achieving the necessary relative phase shifts. Ofcourse, as those in the art will appreciate, the current source 26 couldbe just as well be replaced with a voltage source; however, since thephase shifting and/or other effects to be described herein are believedto be proportional to the d.c. current, the exemplary embodiment hasbeen explained using a variable d.c. current source for explanatorypurposes.

In essence, the exemplary embodiment in FIG. 1 provides for a d.c.electrical current to flow along the isolated segments 28, and 32 of ther.f. feedline structure. It has been discovered, that when d.c. currentsare passed through these microstrip feedlines above the ferrite loadeddielectric, a controlled phase shift may be introduced into r.f. signalsalso passing therealong.

Accordingly, as can be appreciated from FIG. 1, the r.f. signals routedto the microstrip radiator N will not experience any further additionalrelative phase shifts. However, those r.f. signals routed to microstripradiator N will experience an additional phase shift proportional to thecurrent being passed along isolated segment 28 and to the length ofsegment 28.

Likewise, the r.f. signal being passed to radiator N will experience asimilar added relative phase shift (since the d.c. circuit is a seriescircuit exactly the same d.c. current must be flowing in segment 30 asin segment 28) but since the length of segment 30 is twice the length ofsegment 28, these signals will have experienced twice as much relativephase shifting as those which are supplied to radiator N Similarly, thesignals supplied to radiator N undergo a still further phase shift alongsegment 32 of the d.c. circuit which is equal in length to one-half ofsegment 30 and to the full length of segment 28. Accordingly, thesignals reaching radiator N will be shifted three times as much inrelative phase as those signals which are supplied the radiator N Thesegments 28, 30 and 32 of the r.f. feedline in FIG. 1 are isolated fromthe other portions of the r.f. feedline with respect to d.c. currents byd.c. blockingr.f. passing means 34 which are somewhat analogous to thed.c. blocking capacitors used in low frequency electronics circuits.Here, to insure maximum passage of r.f. currents, the plates" of thesecoupling means should be approximately one fourth of a wave length long(taking into account the dielectric and magnetic parameters of theferrite loaded dielectric) and spaced, preferably, no more than two tothree thousandths of an inch apart.

These isolated segments of the r.f. feedline are interconnected by d.c.passing-r.f. blocking means 36, 38 and 40. These d.c. passing-r.f.blocking segments of the d.c. circuit are somewhat analagous to r.f.chokes commonly used in electrical circuits. To minimize theinterference with r.f. currents in the r.f. feedlines, the d.c. circuits36, 38 and 40 should include any necessary open circuited line segments42 dimensioned and spaced to reflect an r.f. open circuit condition atthe actual points of connection to the r.f. feedline for the anticipatedoperating frequency.

Thus, as should now be appreciated, a complete d.c. circuit has beendescribed within the planar or single layer arrangement of electricalconductors 12. This circuit comprises the d.c. passing-r.f. blockingportions 36, 38 and 40 together with the isolated r.f. feedline segments28, 30 and 32. Of course, the d.c. circuit is returned to ground as at44 to complete the electrical circuit.

Referring now to FIG. 3, the situation as it would exist with no currentflowing in the d.c. circuit from current source 26 is shown at the topline of FIG. 3 wherein all four of the microstrip radiators arereceiving equal power and equally phased excitations to result in a beamdirection normal to the plane of the linear array. However, when thecurrent source 26 is activated to produce some current 1 relative phaseshifts will be introduced in the r.f. signals traversing isolatedsegments 28, 30 and 32 which phase shifts will be proportional to themagnitude of the current I, and to the length of r.f. feedlineconducting such d.c. currents along which the various r.f. signals arepropagating. Accordingly, for some value I, a situation can be expectedas shown in line 2 of FIG. 3 where the relative phase angles between theexcitation or driving signals to the four microstrip radiators differ by10 to cause the beam direction to be deviated as shown in the secondline of FIG. 3.

For a further increase in the d.c. current to a second higher value 1 asituation will be reached as depicted in line 3 of FIG. 3 where thearray elements are excited by signals 30 out of phase with respect totheir nearest neighbors to even further deviate the beam direction as isalso indicated in FIG. 3. Accordingly, as should now be apparent, thebeam of the linear array may be swept along the dimension of the array(i.e., rotated with respect to the fixed array) by merely sweeping thecurrent or voltage source 26.

Besides sweeping the beam direction of such an array, it has also beendiscovered that it is possible to change the actual resonant frequencyof the microstrip radiators with this antenna structure as isschematically depicted in FIG. 4. Here, one of the microstrip radiators50 has been connected into a d.c. circuit via the d.c. passing-r.f.blocking segments 52 and 54 with a d.c. current or voltage source 56.Thus, as the d.c. current or voltage source 56 is varied, the ferritematerial is caused to take on different values of magnetic permeabilitywhich will, in turn, change the effective electrical length(approximately one-half wavelength at resonance) of the radiator 50according to the well-known electrical formula )t./2 mwhich, of course,will change the effective resonant frequency of the microstrip radiator50 as should now be apparent. Accordingly, in spite of the fact thatmicrostrip antennas are relative narrow bandwidth radiators, theresonant frequency may be changed by this technique to effectivelyincrease the potential operating bandwidth of the microstrip radiators.

As should now be apparent, the scanning of the resonant frequency of theradiators as depicted for one radiator in FIG. 4 may be utilized with asingle microstrip radiator as shown in FIG. 4 or for one or more of themicrostrip radiators of an array such as, for example, the array of FIG.1.

Since d.c. electrical currents are being utilized within the r.f.feedline of FIG. 1, it is also possible to selectively alter the beamsweeping or scanning operation of the array as a function of the voltageby using switchable diodes such as shown in FIG. 5. The diodes may beZener type diodes which are selectively actuated by various d.c. voltagelevels and/or they may be controllable diodes that are under the controlof a minicomputer or some other conventional control means to altereither the r.f. and/or the d.c. elecrical circuits to obtain furtherselected changes in the relative phase shifts to be attained between thevarious radiators in the array as should now be appreciated by those inthe art.

A two dimensional array of microstrip radiators is depicted in FIG. 6together with an arrangement for scanning the pencil beam of radiationproduced by such a two dimensional array in two coordinate directions.For instance, as shown in FIG. 6, four linear arrays 100, 102, 104 and106 may be placed side by side to provide the two dimensional array.Each of the linear arrays includes a corporate structured r.f. feedlineas shown in FIG. 1 together with appropriate d.c. circuits for scanningthe beam in the X direction (that is between the bottom and top of FIG.6) in response to variations in the I, current from current source 108as should now be apparent from the previous discussion.

In addition, each of the r.f. inputs 110, 112, 114 and I16 are carriedupward to another corporate structured r.f. feedline which includes ad.c. electrical circuit by which the relative phases of the r.f. signalsbeing input to each of the linear arrays may be selectively shifted forcausing the beam to scan in the Y direction between left and right inFIG. 6). That is, selective phase changes proportional to the current1,, from current source 118 are introduced for r.f. signals traversingthe isolated r.f. feedline portions 120, I22 and 124, which isolatedsegments are interconnected by d.c. passing-r.f. blocking circuits 126,128 and 130 as shown in FIG. 6.

The operation of the two dimensional array is exactly analagous to theone dimensional array previously discussed and it should now be apparentthat a pencil beam of radiation produced by the two dimensional 5 arraymay be selectively directed to any desired direction along the X and Ycoordinates by selectively choosing the appropriate current magnitudesfor current I, and I from current sources 108 and 118 respectively.

Although only a few specific embodiments of this invention have beendescribed in detail above, those in the art will readily appreciate thatthere are many possible modifications to the exemplary embodimentswithout departing from the spirit and teaching of this invention.Accordingly, this invention is intended to encompass all suchmodifications and/or variationsv What is claimed is:

1. An antenna structure comprising:

an electrically conducting ground surface,

a single layer arrangement of electrical conductors including at leastone r.f. radiator and r.f. feedline connected thereto,

a dielectric layer loaded with a ferrite material disposed between saidground surface and said single layer arrangement, and

said single layer arrangement including d.c. circuit means for passingd.c. electrical current through at least a predetermined portion of saidelectrical conductors.

2. An antenna structure as in claim 1 wherein said d.c. circuit means isconnected to said r.f. radiator whereby the resonant frequency of theradiator can be controlled by controlling the permeability of saidferrite material via the d.c. electrical current passing therethrough.

3. An antenna structure as in claim 2 wherein said d.c. circuit meanscomprises r.f. blocking-d.c. passing means for connecting said radiatorinto a complete d.c. electrical circuit. 40 4. An antenna structure asin claim 1 wherein said d.c. circuit means is connected to said r.f.feedline whereby controlled phase shifts in r.f. energy travellingtherealong can be achieved by controlling the d.c. electrical currentpassing therethrough.

5. An antenna structure as in claim 4 wherein said d.c. circuit meanscomprises:

d.c. blocking-r.f. passing means disposed in said r.f.

feedline for isolating predetermined portions of the r.f. feedline withrespect to d.c. electrical currents,

50 and r.f. blocking-d.c. passing means disposed for interconnectingsaid isolated portions into a complete d.c. electrical circuit. 55 6. Anantenna structure as in claim 5 wherein said d.c. blocking-r.f. passingmeans comprises:

two closely spaced but physically separated parallel electricalconductors within said single layer arrangement. I 7. An antennastructure as in claim 5 wherein said r.f. blocking-d.c. passing meanscomprises:

electrical conductors including open circuited stubs disposed to reflectan r.f. open circuit condition at an anticipated r.f. operatingfrequency where connections are made with the r.f. feedline. 8. Anantenna structure as in claim 1 wherein: said at least one r.f. radiatorcomprises a plurality of r.f. radiators disposed to form a phasedantenna array providing a beam pattern of radiation along apredetermined direction,

said r.f. feedline comprises a corporate structure feedline for dividingan r.f. input energy between the r.f. radiators at predeterminedrelative phase angles in the absence of said do. electrical current, and

said d.c. circuit means includes d.c. electrical current paths alongselectively predetermined portions of the r.f. feedline to control saidrelative phase angles as a function of said do electrical currentwhereby the predetermined direction of said beam patterns of radiationis controlled.

9. An antenna structure as in claim 8 wherein said d.c. circuit meanscomprises:

d.c. blocking-r.f. passing means disposed in said r.f. feedline forisolating predetermined portions of the r.f. feedline with respect tod.c. electrical currents, and

r.f. blocking-dc passing means disposed for interconnecting saidisolated portions into a complete dc electrical current circuit.

10. An antenna structure as in claim 8 wherein:

said plurality of r.f. radiators are disposed in a two dimensionalphased array, and

said d.c. circuit means comprises:

a first d.c. circuit for passing a first d.c. electrical current tocontrol the predetermined direction of the beam pattern in acorresponding first coordinate direction, and

a second d.c. circuit for passing a second d.c. electrical current tocontrol the predetermined direction of the beam pattern in acorresponding sec ond coordinate direction.

11. An antenna structure as in claim 8 further comprising controllableswitch means connected to at least one of said r.f. feedline and saidd.c. circuit means for providing further selectable changes in therelative phase of r.f. energy provided to said r.f. radiators.

12. An antenna structure as in claim 11 wherein said controllable switchmeans comprises at least one diode.

1. An antenna structure comprising: an electrically conducting groundsurface, a single layer arrangement of electrical conductors includingat least one r.f. radiator and r.f. feedline connectEd thereto, adielectric layer loaded with a ferrite material disposed between saidground surface and said single layer arrangement, and said single layerarrangement including d.c. circuit means for passing d.c. electricalcurrent through at least a predetermined portion of said electricalconductors.
 2. An antenna structure as in claim 1 wherein said d.c.circuit means is connected to said r.f. radiator whereby the resonantfrequency of the radiator can be controlled by controlling thepermeability of said ferrite material via the d.c. electrical currentpassing therethrough.
 3. An antenna structure as in claim 2 wherein saidd.c. circuit means comprises r.f. blocking-d.c. passing means forconnecting said radiator into a complete d.c. electrical circuit.
 4. Anantenna structure as in claim 1 wherein said d.c. circuit means isconnected to said r.f. feedline whereby controlled phase shifts in r.f.energy travelling therealong can be achieved by controlling the d.c.electrical current passing therethrough.
 5. An antenna structure as inclaim 4 wherein said d.c. circuit means comprises: d.c. blocking-r.f.passing means disposed in said r.f. feedline for isolating predeterminedportions of the r.f. feedline with respect to d.c. electrical currents,and r.f. blocking-d.c. passing means disposed for interconnecting saidisolated portions into a complete d.c. electrical circuit.
 6. An antennastructure as in claim 5 wherein said d.c. blocking-r.f. passing meanscomprises: two closely spaced but physically separated parallelelectrical conductors within said single layer arrangement.
 7. Anantenna structure as in claim 5 wherein said r.f. blocking-d.c. passingmeans comprises: electrical conductors including open circuited stubsdisposed to reflect an r.f. open circuit condition at an anticipatedr.f. operating frequency where connections are made with the r.f.feedline.
 8. An antenna structure as in claim 1 wherein: said at leastone r.f. radiator comprises a plurality of r.f. radiators disposed toform a phased antenna array providing a beam pattern of radiation alonga predetermined direction, said r.f. feedline comprises a corporatestructure feedline for dividing an r.f. input energy between the r.f.radiators at predetermined relative phase angles in the absence of saidd.c. electrical current, and said d.c. circuit means includes d.c.electrical current paths along selectively predetermined portions of ther.f. feedline to control said relative phase angles as a function ofsaid d.c. electrical current whereby the predetermined direction of saidbeam patterns of radiation is controlled.
 9. An antenna structure as inclaim 8 wherein said d.c. circuit means comprises: d.c. blocking-r.f.passing means disposed in said r.f. feedline for isolating predeterminedportions of the r.f. feedline with respect to d.c. electrical currents,and r.f. blocking-d.c. passing means disposed for interconnecting saidisolated portions into a complete d.c. electrical current circuit. 10.An antenna structure as in claim 8 wherein: said plurality of r.f.radiators are disposed in a two dimensional phased array, and said d.c.circuit means comprises: a first d.c. circuit for passing a first d.c.electrical current to control the predetermined direction of the beampattern in a corresponding first coordinate direction, and a second d.c.circuit for passing a second d.c. electrical current to control thepredetermined direction of the beam pattern in a corresponding secondcoordinate direction.
 11. An antenna structure as in claim 8 furthercomprising controllable switch means connected to at least one of saidr.f. feedline and said d.c. circuit means for providing furtherselectable changes in the relative phase of r.f. energy provided to saidr.f. radiators.
 12. An antenna structure as in claim 11 wherein saidcontrollable switch means comprises at least one diode.